In oil/gas wells, water or steam is often injected into the oil/gas field to increase production. It is desired to provide information about the flow conditions in the water/steam injection lines available. However, there are only a limited amount of flow meters available for downhole applications which are very expensive, bulky and complex, see for example the system described in U.S. Pat. No. 6,691,584 B2.
Besides, JP200387451 (Hishida Yasuyuki) describes an optical flow-velocity sensor, wherein a flow induced bending of a flexible detecting rod bending in the direction of the flow is being detected using fiber Bragg gratings. Calibration of this sensor will be relatively hard due to its configuration, since the dependency between bending and flow rate is non-linear, and, moreover, an additional Bragg grating is required to provide for temperature compensation. Besides, this sensor is not very accurate due to the type of measurement (measuring strain using the amplitude of a FBG reflected sensor signal) and since the flexibility of the rod may change over time, leading to a drift in the measurement over time. Besides, this sensor is not sufficiently suitable to be used in downhole applications.